In late years, “touch panels” have come to be widely used which are installed on surfaces of flat panel displays (FPD) included in a mobile phone, a portable device for electronic documents, a vending machine, a car navigation system, and the like.
The “touch panels” described above are largely divided into resistive ones and capacitive ones. The “resistive touch panel” has a main part which includes a transparent substrate formed of a resin film, an X-coordinate-(or Y-coordinate-) detecting electrode sheet and a Y-coordinate- (or X-coordinate-) detecting electrode sheet provided on the substrate, and an insulating spacer provided between these sheets. Here, although the X-coordinate-detecting electrode sheet and the Y-coordinate-detecting electrode sheet described above are spatially separated, both coordinate-detecting electrode sheets are configured to come into electrical contact with each other when pressed by a pen or the like, and to detect the position (X-coordinate and Y-coordinate) which the pen touched. The sheets are designed to trace the movement of the pen and recognize its coordinates, making it possible for the character to be inputted as a result. On the other hand, the “capacitive touch panel” has a structure where an X-coordinate- (or Y-coordinate-) detecting electrode sheet and a Y-coordinate- (or X-coordinate-) detecting electrode sheet are laminated with an insulating sheet in between, and an insulator such as glass is dispose on these. With this setup, when a finger approaches the above-described insulator such as glass, the sheets detect the position because electric capacitances of the X-coordinate-detecting electrode and the Y-coordinate-detecting electrode change.
Conventionally, transparent conductive films formed of ITO (indium oxide-tin oxide) and the like have been widely used as a conductive material for a circuit pattern of electrodes and the like (see Patent Document 1). Along with an increase in size of touch panels, mesh-structure metal thin lines as disclosed in Patent Document 2, Patent Document 3, and the like are beginning to be used.
Here, comparison between the transparent conductive film and the metal thin line described above shows the transparent conductive film has an advantage that, due to its excellent transmittance in a visible wavelength range, the circuit pattern of electrodes and the like is less visible, but the transparent conductive film has a disadvantage that it is unsuitable for the purpose of increasing the size and response speed of touch panels because its electrical resistance value is higher than that of the metal thin line. The metal thin line, on the other hand, is suitable for the purpose of increasing the size and response speed of touch panels because of its low electrical resistance value, but has a disadvantage that, due to a high reflectance in the visible wavelength range, the circuit pattern may be visible under highly bright illumination even if the metal thin line is formed into a fine mesh structure, which results in a decrease in product value.
A possible method of reducing the reflectance of the metal thin line in the visible wavelength range is to combine a metal film and a dielectric multilayered film to create an anti-reflective film. However, the method of combining the metal film and the dielectric multilayered film is not preferable because the metal thin line for the circuit pattern of electrodes and the like is formed by etching.
In such a technical background, a method has been proposed which reduces reflection on the metal film observed from the resin film side by, for example, forming a blackened layer between the resin film and the metal film by electrolytic plating or the like (see Patent Document 4), or providing a light absorbing layer (metal absorption layer) made of a metal oxide between the resin film and the metal film (see Patent Document 5).